Xenserver and Storage
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@jrc said in Xenserver and Storage:
Can someone give me an overview what a VSAN setup would physically and software wise look like. Sounds like there is a controller involved, would this run on the host? Both hosts? Stand alone hardware?
It's SAN run on the hosts. VSAN just standard for Virtual SAN. It's really SAN, but it doesn't have any appliance associated with it, so you don't take on all of the risks of external storage, because it is stored on the hypervisor.
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@jrc you'd have a VM on each host, running the VSAN software. They'd pool the resources from all of your servers.
Only your hypervisors would be the things needed. No dedicated cabling between the systems, no custom switches, no external storage.
Everything is hyperconverged between your available servers.
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If you put VSAN on stand alone hardware, it turns back into normal SAN.
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So you have a VM on each host, and you give it all the local storage. It then allows you to connect the host to it via some protocol (iSCSI, NAS etc)? Or does the VM has some sort of extra hook into the OS to manage and share the storage?
Does it basically just keep the storage volumes on each host synced and identical?
What kind of overhead does this create (ie if I have 6Tb in each server, does that mean I actually only have 3Tb of usable space since I need 2 copies of everything, 1 for each server)?
Is there a need for a dedicated link between hosts for sync traffic?
Starwind's stuff is free, which is cool. Is the paid version particularly expensive? I am thinking support would be a good idea, if only for a year.
This just sounds too easy and/or good to be true. As it sounds like I just need to add drives to my 2 hosts and setup some free software and I'd be set. So I am just making sure I know about as many of the considerations as possible before I run this up the flag pole for a budget.
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@jrc said in Xenserver and Storage:
So you have a VM on each host, and you give it all the local storage. It then allows you to connect the host to it via some protocol (iSCSI, NAS etc)?
It is VSAN if it uses iSCSI. It is VNAS if it uses NFS or SMB.
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@jrc said in Xenserver and Storage:
Or does the VM has some sort of extra hook into the OS to manage and share the storage?
That would not be VSAN then. It's really SAN. Not something randomly being called SAN. It's just a SAN that isn't on its own hardware.
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@jrc said in Xenserver and Storage:
Is there a need for a dedicated link between hosts for sync traffic?
Yes, just like with normal SAN.
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@jrc said in Xenserver and Storage:
Starwind's stuff is free, which is cool. Is the paid version particularly expensive? I am thinking support would be a good idea, if only for a year.
Not too bad. Way less than something like VMware's VSAN.
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@scottalanmiller said in Xenserver and Storage:
@jrc said in Xenserver and Storage:
Or does the VM has some sort of extra hook into the OS to manage and share the storage?
That would not be VSAN then. It's really SAN. Not something randomly being called SAN. It's just a SAN that isn't on its own hardware.
So the appliance then makes use of the virtual hard drives you assign to it for the storage your host then uses? How do you get past the 2Tb limit in this then??
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@jrc said in Xenserver and Storage:
This just sounds too easy and/or good to be true. As it sounds like I just need to add drives to my 2 hosts and setup some free software and I'd be set. So I am just making sure I know about as many of the considerations as possible before I run this up the flag pole for a budget.
Don't think of it that way. This is exactly what we've been preaching for forever. When we say "no one needs a SAN", this stuff is why and long has been. This is just one of the ways to have RLS... you can see when I was writing about RLS:
http://www.smbitjournal.com/2013/07/replicated-local-storage/
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@jrc said in Xenserver and Storage:
@scottalanmiller said in Xenserver and Storage:
@jrc said in Xenserver and Storage:
Or does the VM has some sort of extra hook into the OS to manage and share the storage?
That would not be VSAN then. It's really SAN. Not something randomly being called SAN. It's just a SAN that isn't on its own hardware.
So the appliance then makes use of the virtual hard drives you assign to it for the storage your host then uses? How do you get past the 2Tb limit in this then??
You don't. Anything on top of Xen is going to have that limit.
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@scottalanmiller said in Xenserver and Storage:
@jrc said in Xenserver and Storage:
@scottalanmiller said in Xenserver and Storage:
@jrc said in Xenserver and Storage:
Or does the VM has some sort of extra hook into the OS to manage and share the storage?
That would not be VSAN then. It's really SAN. Not something randomly being called SAN. It's just a SAN that isn't on its own hardware.
So the appliance then makes use of the virtual hard drives you assign to it for the storage your host then uses? How do you get past the 2Tb limit in this then??
You don't. Anything on top of Xen is going to have that limit.
Then how on earth does that solution scale like they say it does? That means you have a limit of ~32Tb of attached storage (Xen's 16* attached VHD limit and 2Tb per VHD limit). How does the virtual appliance handle getting beyond that?
*I could be remembering the number of attached HDD limit wrong, but I do recall there is one and it is low, but I ran into with Unitrends backups more than once.
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@jrc said in Xenserver and Storage:
What kind of overhead does this create (ie if I have 6Tb in each server, does that mean I actually only have 3Tb of usable space since I need 2 copies of everything, 1 for each server)?
It's network RAID 1 in a two node case. You lose 50% of capacity. But you would with a normal SAN, too. Everything is the same as a normal SAN. So if you have 6TB on each of two nodes, you get 6TB usable by the cluster.
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@jrc said in Xenserver and Storage:
Then how on earth does that solution scale like they say it does?
Starwind can use as many 2TB chunks as you want on any given node. And it can use as many nodes as Xen supports. Starwind will use everything Xen can throw at it.
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@jrc said in Xenserver and Storage:
Then how on earth does that solution scale like they say it does? That means you have a limit of ~32Tb of attached storage (Xen's 16* attached VHD limit and 2Tb per VHD limit). How does the virtual appliance handle getting beyond that?
You have to work around the 2TB limit in another way, but Starwind will use it regardless of how you get it there. So Starwind definitely does not have that limit. But trying to use Xen's 2TB limit system under it will create limits on the Xen side.
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Remember, we say Xen but these limits are 100% XenServer. If you were on Xen, you'd have none of these limits.
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Would spanning the drives within the guest address this issue as far as the guest cares? At 2TB we're discussing file shares and large databases anyways.
Things that simply need storage, continuous or not when "physically" looking at them. Within the guest OS simply address the limit there. . .
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@scottalanmiller said in Xenserver and Storage:
@jrc said in Xenserver and Storage:
Then how on earth does that solution scale like they say it does? That means you have a limit of ~32Tb of attached storage (Xen's 16* attached VHD limit and 2Tb per VHD limit). How does the virtual appliance handle getting beyond that?
You have to work around the 2TB limit in another way, but Starwind will use it regardless of how you get it there. So Starwind definitely does not have that limit. But trying to use Xen's 2TB limit system under it will create limits on the Xen side.
I'm sorry of this sounds dense, but what??
(And yeah, I realize when We/I say Xen we mean Xenserver and not pure Xen).
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@dustinb3403 said in Xenserver and Storage:
Would spanning the drives within the guest address this issue as far as the guest cares? At 2TB we're discussing file shares and large databases anyways.
Things that simply need storage, continuous or not when "physically" looking at them. Within the guest OS simply address the limit there. . .
That's true. But only to the total limit that XenServer can provide.
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@scottalanmiller said in Xenserver and Storage:
@dustinb3403 said in Xenserver and Storage:
Would spanning the drives within the guest address this issue as far as the guest cares? At 2TB we're discussing file shares and large databases anyways.
Things that simply need storage, continuous or not when "physically" looking at them. Within the guest OS simply address the limit there. . .
That's true. But only to the total limit that XenServer can provide.
Which the limits are listed here.
255 virtual drives per VM (assuming the guest OS can support it). So at the most for a single VM you could have 521,220 TB's worth of space. . .
